1. Field of the Invention
This invention relates to thermoplastic articles molded from a heterogeneous blend of incompatible polymers. Especially preferred polymers are a polyolefin first polymer and a second polymer, incompatible with the polyolefin. The invention, additionally, relates to processes for making such articles. The invention specifically relates to such articles having substantially uniform wall thicknesses around the circumference of a generally cylindrical shape with resulting improved barrier properties and strength.
2. Description of Prior Art
U.S. Pat. No. 4,410,482 discloses manufacture of thermoplastic articles from a heterogeneous blend of a polyolefin first polymer and an incompatible second polymer. The articles of that patent have the polymer components present as a multitude of thin, substantially two-dimensional, parallel and overlapping layers and such articles in the form of containers are disclosed to exhibit permeation barrier characteristics greatly increased in comparison with containers made from polyolefin, alone. Other patents which disclose articles having a similar construction include U.S. Pat. Nos. 4,444,817 and 4,416,942.
U.S. Pat. No. 3,099,860 discloses an extrusion device for making tubing of homogeneous wall construction whereby molten molding material is conducted through the device by streamlining support fins to reduce the existence of flow lines caused by separation of the material in the so-called nozzle head. This patent also discloses a steplike offset of the support to assure effective mixing of the molten material.
U.S. Pat. Nos. 3,279,501 and 3,404,203 disclose manufacture of tubing with oriented internal and external surfaces wherein the mold surfaces are counter-rotated during extrusion of the molten material.
U.S. Pat. No. 3,256,560 discloses a die for orienting the internal and external surfaces of an extrudate by means of grooves cut in the respective surfaces of the die to direct the flow of molten material in opposite directions.